There are two known types of plastic paint cans. One type is designed for use with plastic snap-on lids. The other type employs a metal lid with deformable tabs which can be bent to grip a portion of the can. The metal lid is removed by unbending the tabs so that they no longer grip the can.
The plastic paint cans with plastic lids are disadvantageous because the plastic lids can be punctured or ruptured more easily than their metal counterparts. The metal lids with tabs suffer from a relatively short life expectancy because the tabs become permanently deformed or break off when they are bent repeatedly to open and reseal the can.
Because of such deficiencies in the known plastic paint cans, the paint can most widely used at the present is a cylindrical metal container provided with a double-tight metal sealing ring attached to the top rim of the can. The primary advantage of this old design, which best accounts for its enduring popularity, is that the double-tight sealing ring affords an excellent seal which can be opened and resealed repeatedly, without encountering any of the problems discussed above.
Heretofore, nobody has developed a plastic paint can having a double-tight metal sealing ring. One reason for the lack of such a development in the past is that very few container manufacturers have the expertise in the plastic and metal technologies necessary to produce the plastic can and the double-tight metal sealing ring. Also, the manufacturing companies possessing the sophisticated metal technology required to make the metal sealing rings would rather market a product manufactured entirely of metal, so that they could provide the metal can as well as the metal sealing rings. For a similar reason, manufacturers of plastic paint cans prefer to produce an all plastic product.
Notwithstanding the popularity of the metal paint cans with double-tight metal sealing rings and their extensive use in the paint industry, these cans do suffer from some rather significant disadvantages. What follows is a brief discussion of three of the more prevalent and serious disadvantages.
First, the conventional double-tight cylindrical metal can is expensive to produce because of the cost involved in purchasing the sheet metal from which the can is fabricated and in coating the can to prevent rust. Storage and transportation of the cans are complicated due to their weight and shape, which prevents them from nesting one inside another.
A rust preventer is applied to the sheet metal used to make the double-tight sealing ring, but cutting of the sheet metal to form a ring blank from which the sealing ring is formed leaves a raw uncoated inner end of metal which can become rusty. Thus, a second problem is that the paint can be discolored by rust which forms on the inner edge of the sealing ring and falls into the paint. Numerous elaborate efforts have been made to prevent the inner edge of the sealing ring from rusting. These efforts, for the most part, have been ineffective or expensive, so that the problem persists to this day.
A third problem is that the underside of the double-tight sealing ring tends to collect paint which then dries and, over a period of time, becomes brittle. Then, when the can is reopened, the dry brittle paint on the underside of the sealing ring will sometimes break apart and fall into the paint, making it necessary to strain the paint before using it.